1. Field of the Invention
This invention relates to catalysis and, in particular, to catalysis by compounds containing Group VIII metals.
2. Art Background
Metal alloys formed from metals such as platinum and rhenium, or nickel and palladium are employed as catalysts in a wide variety of commercially significant reactions. For example, these alloys are utilized for the reforming of hydrocarbons for gasoline. Production of these metal alloys is usually accomplished by treating a support such as a porous silica or alumina body with a solution of the appropriate metal salts or metal oxides and subsequently reducing these materials in the presence of hydrogen to form the alloy.
Other metal compositions also show catalytic activity for various applications. Presently, investigations concerning intermetallic compounds, e.g., compounds represented by the formula A.sub.x B.sub.y, where A and B are metallic atoms and x and y are integers or fractional values, similarly demonstrate catalytic activity. Intermetallic compounds are prepared initially in bulk from the elements corresponding to the atoms of the final product, by first heating the mixture to form a melt, and then cooling, thus producing the desired intermetallic compound. This bulk compound is then mechanically ground into particles which are used for catalysis.
In reforming processes many intermetallic catalysts yield relatively good conversion of aliphatic, e.g., heptane and cycloaliphatic compounds, such as cyclohexane, to the more desirable aromatic compounds, e.g., toluene and benzene. Despite this desirable performace, bulk intermetallic catalysts have certain limitations. For example, the surface area produced by mechanical procedures is typically less than 1 m.sup.2 /gm. The limited surface area generated by mechanical grinding correspondingly limits the efficacy of the catalyst. Additionally, in processes such as reforming, hydrogen is introduced to prevent the decomposition of the reactant aliphatic compound and the poisoning of the catalyst by carbon deposits resulting from this decomposition. However, the presence of hydrogen also favors the hydrogenolysis of aliphatic compounds such as cyclohexane and retards the preferable dehydrogenation of these compounds to aromatic compounds such as benzene. Yet, for many applications an enhanced degree of dehydrogenation relative to hydrogenolysis in the presence of hydrogen together with an enhanced conversion efficiency is certainly desirable.